To study the possibility of cross-species transmission of CWD, two species of nonhuman primates, squirrel monkeys and cynomologus macaques, were infected orally or intracerebrally with brain material derived from CWD affected deer or elk. At the conclusion of FY10 thirteen of thirteen intracerebrally infected squirrel monkeys had developed clinical neurological signs and were confirmed by biochemical and pathological testing of brain to have a prion disease. Eight orally infected squirrel monkeys have also developed disease, three remain asymptomatic. To this point no cynomologus macaques have developed any signs of disease regardless of inoculation route (all macaques were inoculated >7 years ago). Observations on the remaining monkeys will continue. During FY08 four additional cynomologus macaques and squirrel monkeys were inoculated with brain homogenates derived from a CWD infected squirrel monkey to evaluate the ability of CWD to adapt to a nonhuman primate host. During FY10 both squirrel monkeys inoculated with squirrel monkey adapted CWD developed disease. The incubation period from this inocula was much faster and clinical signs were slightly different suggesting adaptation to a new host or a higher titer of inocula. The successful passage of CWD derived from a squirrel monkey into additional squirrel monkeys confirms the presence of prion infectivity. This confirmation was important since the same squirrel monkey CWD inocula did not cause disease in transgenic mice expressing human or deer prion protein. The lack of transmission to the "humanized" mice is encouraging data that supports the conclusion that CWD will likely not infect humans. In addition to testing infected squirrel monkey brain we are also evaluating blood from infected squirrel monkeys for the presence of prion infectivity. None of these monkeys have shown any signs of disease at the close of FY10.